1. Field Of The Invention
The present invention pertains generally to circuit breakers and, more particularly, to multipole circuit breakers.
2. Description Of The Related Art
A single pole circuit breaker is a device which serves to interrupt electrical current flow in an electrical circuit path upon the occurrence of an overcurrent in the circuit path. On the other hand, a multipole circuit breaker is a device which includes two or more interconnected, single pole circuit breakers which serve to substantially simultaneously interrupt current flow in two or more circuit paths upon the occurrence of an overcurrent in any one circuit path.
An example of a single pole circuit breaker of the type used in conventional multipole circuit breakers is depicted in FIG. 1. As shown, the single pole circuit breaker 10 includes an electrically insulating casing 20 which houses, among other things, stationarily mounted terminals 30 and 40. In use, these terminals are electrically connected to the ends of the electrical circuit which is to be protected against overcurrents.
As is known, the casing 20 also houses a stationary electrical contact 50 mounted on the terminal 40 and an electrical contact 60 mounted on a contact bar 70. Significantly, the contact bar 70 is pivotably connected via a pivot pin 80 to a stationarily mounted frame 100. A helical spring 85, which encircles the pivot pin 80, pivotally biases the contact bar 70 toward the frame 100. A contact bar stop pin 90, mounted on the contact bar 70, limits the pivotal motion of the contact bar relative to the frame. By virtue of the pivotal motion of the contact bar 70, the contact 60 is readily moved into and out of electrical contact with the stationary contact 50.
An electrical coil 110, which encircles a magnetic core 120 topped by a pole piece 130, is positioned adjacent the frame 100. An electrical braid 140 serves to electrically connect the terminal 30 to one end of the coil 110. An electrical braid 150 connects the opposite end of the coil 110 to the contact bar 70. Thus, when the contact bar 70 is pivoted in the clockwise direction (as viewed in FIG. 1), against the biasing force exerted by the spring 85, to bring the contact 60 into electrical contact with the contact 50, a continuous electrical path extends between the terminals 30 and 40.
As is conventional, the circuit breaker 10 also includes a handle 160 which is pivotably connected to the frame 100 via a pin 170. In addition, a toggle mechanism is provided, which connects the handle 160 to the contact bar 70. This toggle mechanism includes a cam link 190 which is pivotably connected to the handle 160 via a pin 180. The toggle mechanism also includes a link housing 200, which itself includes a projecting arm 205, the link housing being pivotably connected to the cam link 190 by a rivet 210 and pivotably connected to the contact bar 70 by a pin 220. The toggle mechanism further includes a sear assembly, including a sear pin 230 which extends through the link housing to the cam link 190. The sear assembly also includes a leg 235, connected to the sear pin 230, and a sear striker bar 240, which is connected to the leg 235 and projects into the plane of the paper, as viewed in FIG. 1. A helical spring 250, which encircles the sear pin 230, biases the leg 235 of the sear assembly into contact with the leg 205 of the link housing, thereby biasing a planar surface on the sear pin 230 into engagement with a step on the cam link 190. It is by virtue of this engagement that the toggle mechanism is locked and thus capable of opposing and counteracting the pivotal biasing force exerted by the spring 85 on the contact bar 70, thereby maintaining the electrical connection between the contacts 50 and 60.
By manually pivoting the handle 160 in the counterclockwise direction (as viewed in FIG. 1), the toggle mechanism, while remaining locked, is translated and rotated out of alignment with the pivotal biasing force exerted by the spring 85 on the contact bar 70. This biasing force then pivots the contact bar 70 in the counterclockwise direction, toward the frame 70, resulting in the electrical connection between the contacts 50 and 60 being broken. Manually pivoting the handle 160 in the clockwise direction then serves to reverse the process.
The single pole circuit breaker 10 also includes an armature 260, pivotably connected to the frame 100. This armature includes a leg which is positioned adjacent the sear striker bar 240. In the event of an overcurrent in the circuit to be protected, this overcurrent will necessarily also flow through the coil 110, producing a magnetic force which induces the armature to pivot toward the pole piece 130. As a consequence, the armature leg will strike the sear striker bar 240, collapsing the toggle mechanism. In the absence of the opposing force exerted by the toggle mechanism, the biasing force exerted by the spring 85 on the contact bar 70 will pivot the contact bar in the counterclockwise direction, toward the frame 70, resulting in the electrical connection between the contacts 50 and 60 being broken.
Significantly, the single pole circuit breaker 10 also includes a trip lever 270 which is pivotably connected to the frame 100 via a pivot pin 320. As more clearly depicted in FIG. 2, the trip lever 270 is generally U-shaped and includes arms 280 and 290 which at least partially enfold the frame 100. A helical spring 330, positioned between the frame 100 and arm 280 and encircling the pin 320, pivotally biases the trip lever toward the frame 100. A projection 300 of the trip lever 270 is intended for insertion into an aperture 310 of the trip lever of an adjacent single pole circuit breaker. Thus, any pivotal motion imparted to the trip lever 270, in opposition to the biasing force exerted by the spring 330, is transmitted to the adjacent trip lever, and vice versa.
If, for example, an overcurrent flows through the coil 110 of the single pole circuit breaker 10, then, as a result, as described above, the single pole circuit breaker 10 will be tripped, i.e., the contact bar 70 will be pivoted in the counterclockwise direction and the electrical connection between the contacts 50 and 60 will be broken. During this pivoting motion, the pin 220, pivotably connecting the link housing 200 to the contact bar 70, will engage a camming surface 285 on the bottom of the leg 280, thereby applying a torque to the trip lever 270. Consequently, the trip lever 270 will be pivoted away from the frame 100 and toward the armature 260. This pivotal motion will also be imparted to the trip lever of the adjacent single pole circuit breaker via the projection 300. Provided the torque applied by the pin 220 is sufficiently large, then the trip lever of the adjacent single pole circuit breaker will depress the corresponding armature, thereby tripping the adjacent circuit breaker.
While single pole circuit breakers of the type described above are certainly useful, they do have certain limitations. For example, when such a single pole circuit breaker is tripped, the torque exerted by the pin 220 on the trip lever 270 is necessarily limited. As noted, this torque is transmitted by the trip lever 270 to the trip lever of the adjacent single pole circuit breaker, which must then depress the corresponding armature before the corresponding toggle mechanism is engaged and collapsed. Thus, a significant fraction of the developed torque is dissipated in depressing the armature. As a consequence, the number of interconnected, single pole circuit breakers which can be substantially simultaneously tripped is limited, i.e., the number is typically no more than six. In addition, the reliability with which six such interconnected, single pole circuit breakers are tripped is sometimes less than one hundred percent.
Not only does the conventional single pole circuit breaker have the limitations discussed above, but the process of mounting the conventional trip lever 270 onto the frame 100 is relatively difficult and time consuming, and sometimes causes difficulties. That is, during the mounting process, the holes in the legs 280 and 290 of the trip lever 270 (see FIG. 2) are aligned with the corresponding holes in the frame 100, and the pin 320 is then inserted through the aligned holes. The leg 280 is then deformed until it snaps over the pin 320, to permit the spring 330 to be mounted onto the pin 320. While the leg 280 is then bent back toward its original position, the result may be such that the initial deformation is not entirely eliminated or, in some cases, deformation is also imparted to the adjacent leg 290. As a consequence, in operation, the leg 280 alone, or both legs 280 and 290, may, for example, rub against the inner walls of the casing 20, preventing the single pole circuit breaker from tripping at the desired trip point. Alternatively, if the deformation of the leg 280 is not substantially eliminated, then, during operation, the pin 220 may not properly engage the camming surface 285 on the leg 280.
Thus, those engaged in developing multipole circuit breakers have sought, thus far unsuccessfully, a single pole circuit breaker in which, upon being tripped, a relatively large torque is applied to the trip lever, a circuit breaker mechanism which avoids torque dissipation, and a trip lever which is conveniently mounted onto the corresponding frame.